1. Field of the Invention
This patent relates to the field of elastic, flexible, cellular polyurethane polymers. More specifically it relates to improved physical properties of the foams achieved by the use of polyoxyalkylene polyols having terminal oxyethylene blocks and a specified degree of oxyethylation coupled with a minimum limit of primary hydroxyl groups.
2. Description of the Prior Art
The preparation of flexible cellular polyurethane (PUR) polymers by reacting polyisocyanates with polyols and, optionally, chain extenders or cross-linking agents in the presence of blowing agents and catalysts as well as, optionally, auxiliaries and additives is known from numerous patents and literature citations. We should like to refer, for example, to the monographs by J. H. Saunders and K. C. Frisch, "High Polymers Series--vol. XVI," Polyurethanes, parts I and II (Interscience Publishers, New York, 1962 and 1964) and R. Vieweg and A. Hoechtlen, "Plastics Handbook--vol. VII," Polyurethanes, (Carl Hanser Publishers, Munich, 1966).
In all areas of application, flexible polyurethane foams must have a high level of mechanical properties manifested in high breaking elongation, tensile strength, and Grave's tear strength such that they may be used at as low a density as possible and still provide suitable performance.
Optimum utilization of production facilities is facilitated by short setting times of the foams.
It is also known that change in process measures can influence the mechanical properties. The break elongation, for example, can be improved by decreasing the hydroxyl/isocyanate group ratio (index). However, this measure simultaneously lowers the compression hardness ("Plastics Handbook--vol. VII," Polyurethanes, pages 478-486). Such contrary property shifts which are frequently incurred by practice of the prior art are undesirable.